1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device and, particularly, to a manufacturing method of a semiconductor device having a metal silicide film.
2. Description of the Related Art
With the increase of integration density of LSI, the fineness of a contact hole thereof is having been increased and the aspect ratio of contact hole, which is represented by a depth of the contact hole divided by a diameter thereof, is also having been increased. When a conventional metal film of such as aluminum formed by sputtering is used in a semiconductor, it is difficult to obtain an acceptable step coverage. Therefore, the connection resistance becomes high and there is a possibility of breakage of a wiring. Even if a formation of wiring is not impossible, the problem of tendency of breakage of wiring is left as it is due to electro-migration of aluminum caused by electric current flowing therethrough. In order to solve this problem, the tungsten plug method in which contact holes are buried with a tungsten film formed by chemical vapor deposition and can provide a superior step coverage has been proposed. According to the tungsten plug method, a tungsten plug is formed, after a barrier metal formed of titanium for lowering a connection resistance (contact resistance) of a contact hole and titanium nitride for improving the intimate adhesion between titanium and tungsten and preventing immigration of tungsten into a semiconductor substrate is formed by sputtering, forming a tungsten film by chemical vapor deposition to bury the contact hole with tungsten and etching back the tungsten film while leaving tungsten in only the contact hole.
According to this method, however, when the contact hole becomes finer and the aspect ratio thereof becomes larger, it becomes impossible to form a titanium film or a titanium nitride film to a desired thickness in the contact hole by sputtering. Therefore, the contact resistance becomes larger and a semiconductor element is damaged by tungsten.
In order to solve these problems, it has been tried to form a titanium film and a titanium nitride film by chemical vapor deposition (CVD) providing a better step coverage. Particularly, the step coverage of titanium nitride film is superior when it is formed by CVD utilizing thermal reaction and is used popularly. It is usual to bury a contact hole by forming a 3-metal layer including a titanium layer, a titanium nitride film and a tungsten film by CVD. In such method, however, the manufacturing step becomes complicated and a manufacturing cost is increased. In order to solve this problem, it has been proposed to bury the contact hole with only the titanium film and the titanium nitride film by removing the step of forming the tungsten film.
FIGS. 4(a) to 4(d) are cross sections of a semiconductor wafer, showing the above mentioned conventional manufacturing steps of burying a contact hole. First, on a silicon substrate 301 in which an element is formed, a BPSG film 302 in the form of a silicon oxide film containing phosphor or boron is formed as an inter-layer insulating film by CVD. Thereafter, a contact hole is formed up to a surface of the element by using a usual photolithography and dry-etching technique (FIG. 4(a)). A diameter of the contact hole may be about 0.4 .mu.m.
Then, the contact hole is completely buried by forming a titanium film 303 to a thickness of 10.about.50 nm by plasma CVD and a titanium nitride film 305 to a thickness of 0.3 .mu.m by usual thermal CVD (FIG. 4(b)). The titanium film 303 reacts with the silicon substrate and a titanium silicide film 304 is formed by heating the semiconductor substrate to a temperature of 500.degree. C. or higher.
Thereafter, the titanium film 303 and the titanium nitride film 305 on the BPSG film 302 are removed by dry-etching using chloride gas while leaving portions of the titanium silicide film 304 and the titanium nitride film 305 in only the contact hole (FIG. 4(c)).
Then, an aluminum alloy film 306 is deposited on the BPSG film 302 by sputtering and patterned to a desired shape by using photolithography and dry-etching technique, resulting in an aluminum wiring (FIG. 4(d)).
In the conventional manufacturing method of semiconductor device mentioned above, however, a large tensile stress of 8E10 dyne/cm.sup.2 or more is exerted on the titanium nitride film formed by CVD and burying the contact hole, when the titanium nitride film is thick. Further, the adhesion of the titanium film to the titanium nitride film formed by thermal CVD is not favorable. For these reasons, the titanium nitride film may be cracked or peeled off from the titanium film. When the titanium nitride film is peeled off from the titanium film, the underlying inter-layer insulating film (BPSG film) may be abnormally etched in the subsequent etching step of the titanium nitride film, so that the manufacturing yield is lowered and the reliability of a resultant semiconductor device is lowered. Further, the peeled titanium nitride film portion becomes immigrant which is also a cause of degradation of yield. When the titanium nitride film is cracked, the abnormal etching of the underlying layer may occur.
In order to solve the above problem, in lieu of the formation of the titanium nitride film 305 by depositing it on the titanium film 303 as shown in FIG. 4(b), it may be considered that, after the titanium film 303 and hence the titanium silicide film 304 are formed, the titanium film 303 is etched away such that only the titanium silicide film 304 is left and, thereafter, the titanium nitride film 305 is deposited.
The conventional method for selectively removing only the titanium film 303 by etching uses a mixture of aqueous ammonia and aqueous hydrogen peroxide. The selective etching step takes a substantial time since it requires, in addition to several minutes for selective removing, a washing time (about 10 minutes) after the etching step, a drying time (about 5 minutes) by a spin dryer, etc. Further, it is clear that there is a problem of a large amount of waste liquid.